I have a Copland 501, and this design is close to the 401. I have done capacitor upgrade - but will like to do a similar upgrade to "better" resistors.

And what brand or type of resistor too choose carbon, tantalum or...

SY

27th March 2005 12:38 PM

By far, the most critical are plate resistors (use non-inductive wirewound for lowest noise and VCR) and feedback resistors.

analog_sa

27th March 2005 01:10 PM

Feedback resistors (R17/R14) and grid stoppers will probably be as far as i would go - no point to go crazy improving this circuit.

As the quality of the voltage used for fixed bias is very audible (really marginal in this design) i would spend some some attention on it. A small choke will be very nice and probably good quality caps bypassing R29/R30.

P1-P3, and yeah anything in the signal path or that will bring down other things on faliure (open or shorted). Carbon film is fine, except for the bias pots, which should technically be something better than conductive plastic (i.e. cermet or WW), but I haven't had any problems there either.

Quote:

Originally posted by analog_sa As the quality of the voltage used for fixed bias is very audible

Huh? Howso? (Assuming the driver is something stiff like 12AU7/6DJ8/6SN7, and the grid leaks are reasonably large (100k or so).)

Tim

analog_sa

28th March 2005 08:23 AM

Quote:

Huh? Howso?

Sorry, i should have been clearer. Only audible to those willing to listen.